where \(\theta \)  is the polar angle of the baryon in the \(e^+e^-\)  c.m. frame
and \(\beta = \sqrt{1-4m_{B}^2/s}\)  is the speed of baryon.
The Gamov-Sommerfeld factor \(C\)  [1]}, [2]}, [3]}
describes the Coulomb enhancement effect: for charged baryon pair
\(C = y/(1-\mathrm {e}^{-y})\)  with \(y = \pi \alpha \sqrt{1-\beta ^{2}} / \beta \) ,
accounts for the electromagnetic interaction between the outgoing baryons;
while for neutral baryon pair \(C=1\) .
The form factors, \(G_E\)  and \(G_M\) , essentially describe the
electric and magnetic distributions inside the baryon and
basically provide a measure of its boundary or size.
These are functions of the four-momentum transfer \(s=q^2\) ,
so more accurately should be written as \(G_E(q^2)\)  and \(G_M(q^2)\) .
In the time-like domain, the form factors are complex
with a nonzero imaginary part, and the translation into the
internal structure is not straightforward, in contrary to
the case in the space-like region. It is noteworthy that
final-state interactions become prevailing close to threshold
and thus should be properly dealt with.
By definition the electric and the magnetic form factors
are equal at the baryon-antibaryon pair's mass threshold
where only \(s\) -wave production contributes [4]},
i.e., \(G_E(4m_B^2)=G_M(4m_B^2)\) ,
but generally they are not.
In analyses of data with limited statistics it is often
assumed that they are equal and the two form factors are replaced
by an effective form factor, \(G_{eff}=G_E=G_M\) .
